The transition states and reaction products for the reaction of carbonyl dibromide (CBr2O) with water have been examined using quadratic configuration interaction (QCISD) methods. There are two competition steps in the reaction of CBr2O with water. The first involves addition of water across the carbonyl oxygen of CBr2O to produce Br2C(OH)(2). The barrier to elimination of HBr and BrC(O)OH from Br2C(OH)(2) is predicted to be quite high, i.e., 39.8 kcal mol(-1), suggesting that Br2C(OH)(2) could be a sink for bromine. The second pathway involves a four-center transition state where the OH of water is added across the carbon bromine bond of CBr2O, eliminating HBr and producing bromoformic acid (BrC(O)OH). Bromoformic acid can proceed to decompose to CO2 and HBr. Overall, the reaction of CBr2O with H2O is predicted to yield CO2 and HBr. (C) 2002 Elsevier Science B.V. All rights reserved.